Gasification of carbonaceous materials containing volatile constituents



Dec. 15, 1953 J. c. KALBACH 2,562,316

GASIFICATION OF CARBONACEOUS MATERIALS CONTAINING VOLATILE CONSTITUENTSFiled July 20, 1948 2 Sheets-Sheet 1 8 CARBON/Z47? GA 8 CHAR STE/141$OXYGEN G 2/ l STEAM j INVENTOR. ufo ch14 5 CH TTOBNEYS Patented Dec. 15,1953 PATENT OFFICE 2,662,816 commands on CARBONACEOUS mire;

RIALS CONTAINING VOLATILE CONSTIT-" John to. Kalbach; New York, N.-;tasslgnor to Hydrocarbon Research lnc New York; N. Ya, a corporation of.New Jersey Application July 20', 1948; Sheerness-732 2* Claims. (01.4"si'--2"62) This invention relates to the" gasificati'on of a solidcarbonaceouszmaterial- The process of the invention is applicable to"gasification of coal, lignite, oil shale and the like- It isparticul'alrly useful for treatment of those carbonaceous ma.- 5 terialscontaining volatile constituents which tend to agglomerate on heating,vparticularly a coking coal.

The fluidized solids technique has been at) plied to processes for the:ga'sific'ation oi carbonatceous materials. Pulverized coal for example,may be treated in a fluidized becl witlr hotinert gases to efifectremoval of volatile? constituents or with an oxidizing gas forgasification toany' de-' sired. extent. Some di fliculty' is experiencedinfluidization of some of the softer coals due to their tendency tobecome plastic or tacky onheating causing agglbmer'ation of the"particles: Coal may be treated prior to g asification to preventagglonieration. Such pretreatment may consist of heating the-- coartodriveoffi a portion of the volatile constituentstherefrom or partialpreoxidation of the coal-with a n oiiygen con-tain" g gas; nitric acid, orother oxidizing agent.- expedient which is used: to some extent involvesadmixing the raw-coal With char, ash; or sa-ntt to prevent agglomerationof the raw eo'al particles:

Gasificatiom of carbonaceous mate als containing volatile eonstituentsmay be acc'orr'iplished' by' heating, by chemical combinationor bi acombination of both. A somewhat elevated tern? perature: is required forgasification, asis now-r 1 in thenart. The fluidiz'd b'ed technique-aidsn maintaining the desired. temperature" conditions" Within" ratherclose: limits; I I

The process. of the ptesent inventibn is adapt able; to handling-s ofcoking coals and: the like without difiiculty' dueeto agglomeratingtendency of themater-ial and Without" preliminary new ment. I

The process: of the presentinvention involves ca'rbon'izationof the reedmaterial -and gasifiEa-f tion by the concurrent reaction with ox genndsteam. In carbol fizaition; the volatile'constituents' are driven-011 byhattb producea char or coke residue. Gasi c'aiti'onof the-'ca-rboniz'd mteria-l may be. carried? to substantialf complemenleaving only ash orlbw. carbom content cha r as the residual solid:

In" accordance with; this invention, the solid carbonaceous material;iscommiriuted to a ticle size suitable: for fluidizationygenerallv'lessthan oneequarte'r inclri in; diameter; and preferably less than about051 menm diameter; and charged into an agitated mass of particles ofihotmaterial as typifiy ing thop'eraitiori and applica' char.Carbonizati'omof the feed material in the Q improved process" for thegasifi'cation of Solid carbonaceousmaterial;

A further obj ect' is to provide a; rocess w erein each stepcan becarried out under optimum con ditions for that step: 1

Another object is to provide: a process for" the gasifica'tion of solidcarbonaceous maceriar which is particularly applicable tocarbonization'" and gasification of coal',-lignite;oi1 shale and simmermaterials. I

Still another object is toprovi'dea process f the gasification of solidcarbonaceous mama" s wherein those-material's which tend' t'o sort r-rand glgggomerate on: heating" may" be e'fiectively' han Other? objectsand advantages will be apparent from the following detailed descriptiorrand the accom'panying illustrative drawings? The present invention wille described in de: tail with: reference toeoai as the c'arbonac'eb stions orthe process of this invention. It will be" understood that coalis used as a" specific exam-- ple and that the apparatus and methoddescrilted' are not limited tothe'us'e'of coal as the'carbona ce theeasification of ceous feed materia variousmaterials is ow i 'n'the art,the apple enti'orrto other solidi cation of the resent carbonaceousmaterials vnir be evident" to one" skilled in the artfrbhi the detailed'description of this" invention d illustrative examples of itsapplication otrea mentor coal;

Fig. s a diagrammatic elevatioiiafl view, can lyin cross section} of onefarm of apparatus s able for carryingo ptne process ormyiiwhuoii.

Figa 2 is'fadiagramrnatic elevational vievv, part ly in c'ross s'ection,of an arrangement ofappar'ey tusillustratinga modification or theprocess" of my inv'e'ntion-i- With refer nce tothedrawmg'; grouiidicoalifor? example; is'fetl through line 6 intoa hopper 1';

An inert gas may be supplied to the hopper through line 8 to build uppressure in the hopper. The gas also forms an inert blanket avoidingexplosion hazards. The particulate coal is fed from the hopper into thegasification apparatus by means of a screw conveyor 9.

The gasification apparatus comprises a carbonization zone H, agasification zone [2 and a mixing zone l3 intermediate the carbonizationzone and the gasification zone. In the carbonization zone, thevolatilizable Constituents of the coal are volatilized by heating. Inthe gasification zone I2, the char or devolatilized coal from thecarbonization zone is gasified by reaction with oxygen and steam. Boththe carbonization zone and the gasification zone are operated asfluidized beds. In the mixing zone 7 l3, fresh crushed coal is admixedwith char and with hot product gases from the gasification zone. Thechar may be entrained char or ash carried by the hot product gases orchar recycled from the carbonization zone. Generally, both will bepresent to a greater or lesser extent in the mixing zone. The hot gasesfrom the gasifier suspend the particles of coal and char and carry theminto the carbonization zone. The gases serve as a fluidizing medium inthe carbonization zone to maintain the carbonaceous particles in afluidized bed and aid in the distillation of the volatile constituentsfrom the fresh coal feed.

The quantity of entrained char from the gasification zone may varyconsiderably depending upon design and operating conditions.

When the particles of coal are brought into the mixing zone into thestream of hot gases and suspended char, the turbulent motion of thegases causes rapid mixing of the coal particles and the char. Thisprevents agglomeration of particles of coal on heating and facilitatesfluidization of the entire mass of solids in the carbonization zone.Preferably the mixing zone is a cylindrical conduit operated with a gasvelocity in excess of the terminal velocity of the particles of coal andchar. The ratio of char to fresh feed in the mixing zone may vary withinthe range of from about 3 parts char by weight per part of fresh feed toabout 10 parts char per part of feed. A weight ratio of char to feed ofabout :1 is generally satisfactory.

Char from the carbonization zone is supplied to the mixing zone throughline l4 as controlled by a suitable valve 16, for example, a slidevalve. The char from the carbonization zone is introduced into theproduct gas stream from the gasificition zone at a point upstream fromthe point of introduction of the coal so that the char is admixed withthe gases prior to contact with the fresh feed.

Product char from the carbonization zone is fed through line H intoadmixture with steam in line l8 and passed into the gasification zonel2. A portion of the char from the carbonization zone may be withdrawn,if desired, through line l3 as a high quality product char for otheruse. Oxygen from line 2| is supplied to the gasification zone through aseries of tuyres 22.

Char product from the gasification zone is withdrawn through line 23.Generally, the char product from the gasifier will be of relatively lowcarbon content and contain substantially all of the ash from the feedmaterial. The carbon content may be controlled by control of the extentof gasification in the gasification zone to produce a char of anydesired carbon content (for example, 40 per cent) suitable as fuel forgenera- 4 tion of steam or the like. The char withdrawn from thegasifier may be subjected to further reaction with oxygen to producecarbon monoxide.

Gases from the carbonizer H are passed through a separator 24 to recoverentrained solid particles from the gas stream, and the resulting gas,substantially free from solids, is discharged through line 25. Theseparator 24 may be, for example, a centrifugal type separator capableof removing over 99 per cent of the 70 micron particles. The recoveredsolid particles are returned to the fluidized bed in the carbonizerthrough line 26.

The mixture of gases discharged through line 25 may be treated toseparate sulfur compounds, carbon dioxide, tar, and oil therefrom.Alternatively, the gases from line 25 may be reacted with steam andoxygen to convert the tar, oils and gaseous hydrocarbons to carbonmonoxide and hydrogen. The resulting gases from either mode of proceduremay be used as fuel gas or as a source of feed gas, after suitablepurification and adjustment of the proportions of carbon monoxide andhydrogen, for the synthesis of hydrocarbons.

The apparatus illustrated in Fig. 2 of the drawing is particularlyuseful in generation of fuel gases, but may also be utilized to generateother product gases, e. g., synthesis feed gas. The apparatus isgenerally similar to that of Fig. 1 with some modifications.

With reference to Fig. 2, the gasification apparatus comprises acarbonization zone 3|, a gasification zone 32 and a mixing zone 33.Crushed coal enters the feed hopper 21 through line 28; pressurizing gasis admitted through line 29. Coal from the feed hopper 2'! is fed intoline 34 from which it is introduced to the mixing zone. The coal may beconveyed through line 34 by any suitable means, for example, with astream of gas, suitably a recycle gas produced in the gasificationoperation. Alternatively, a mechanical conveyor may be used. The coalintroduced into mixing zone 33 is admixed with char and hot gases fromthe gasifier 32. The coal is suspended in the gases and carried into thefluidized bed in carbonizer 3|.

Provision may be made in the carbonizer 36 for cooling the char andgases to remove excess heat and thereby control the operatingtemperature. The cooling may be effectively accomplished by indirectheat exchange with water, generating steam. The gaseous efiiuent andentrained carbonaceous particles from the carbonization zone aredischarged through line 31 into a separator 38 wherein the particles areseparated from the gas stream. A cyclone type separator is suitable foruse as separator 38. The resulting gases substantially free fromentrained solids are discharged into product gas line 33. The amount ofentrainment of char in line 31 may vary considerably depending uponoperating conditions.

The char separated in separator 38 may be passed to the mixing zone 33or to the gasification zone 32 through lines 42 and 43 respectively.Generally, char is fed into both the mixing zone and the gasificationzone. The char introduced through line 42 into the mixing zone may besupplemented, if desired, by additional char withdrawn directly from thecarbonizer through line 44. This recycled char is admixed with hot gasand entrained char from th gasification zone 32 and with coal from line34 and returned to the carbonizer 3|.

Char from line 43 is admixed with oxygen and -steam 111 line 46 andpassed into the fluidized bed in the gasifier 32. The oxygen and steamserve as reactants and as fluidizing gases in the gasifier 32. Oxygenmay be admitted separately as in Fig. 1, if desired.

A portion of the product gas from the gasifier 32 is diverted throughline 41 to a separator 48. Entrained char is separated from the productgas by the separator which may suitably be of the cyclone type and thegas is discharged through line 49 into the product gas line 39 forfurther treatment. The separated char may be returned to the gasifiervia lines 5| and 46. The gas stream in line 49 may be quenched byintroduction of a suitable cooling medium, Water, for example, throughline 50. Quenching to a temperature below that at which the water gasshift reaction takes place at an appreciable rate, e. g., below about1500 F., is particularly useful in the generation of fuel gases of highheating value.

Residual char from the gasifier may be taken through line 52 for fuel orother purposes or through line 53 into a supplemental gas generator 54.Gas generator 54 may be, for example, a generator of the burner typewherein the residual char is reacted with a suitable oxygencontaininggas introduced through line 56. The gas from the generator 54 is passedthrough line 51 from which it may join the product gas stream or beseparately treated. The residual solid or ash is discharged from thegenerator through line 58.

It will be obvious that various economies may be effected by utilizingheat contents of the various streams of gases and solids. This may beaccomplished, for example, by passing hot streams in heat exchange withcooler streams or by utilizing heat from the hot gases or solids togenerate steam. These various expedients are known in the art and may beresorted to without departing from the scope of the invention.

The process of the invention is particularly advantageous for thegeneration of fuel gas or synthesis gas from coal in that it providesflexible Operating characteristics such that the temperature of thegasifier and the carbonizer may be at any desired value andsubstantially independent of one another. Normally, where hot gases fromthe gasification zone are utilized as a source of heat for thecarbonization zone, the gasification apparatus is relatively inflexible,the temperature of the two zones being interdependent, asdetermined bythe composition of the coal, the rate of feed of the coal, rate of feedand concentrationof the oxygen, steam, etc.

Heat may be supplied to the carbonizer from the gasifier by way of hotgases or hot carbonaceous solid particles, orboth, passing from. thegasifier to the carbonizer. The quantity of heated solid particlespassing from the gasifier to the. carbonizer may be varied widelydepending upon conditions of. operation. If the gasifier is operatedwith a bed level below the top of the vessel. only those particlesactually carried in the gas stream in the gasifier are, passed. with.the efilnent gas into the carbonizer. On the other hand, when thegasifier is operated full, fluidized particles: from. the gasifier areentrained in the streamer relatively high velocity gases leaving theasifier through. the restricted. transfer line, which. also serves as a.mixing zone for the fresh All. of; the carbonized. particles admixedwith fresh feed may be supplied fromthe gasifier.

Beat for the carbonization step is derived from the materials, i. e;,gases and any entrained solids, from the gasification zone. Heatis'supplied to the carbonizer by heat transfer between these materialsand thecarbonaceous feed. Also, in many instances, heat may be suppliedthe carbonizer as a result of exothermic reactions of the gases. Theformation of methane sometimes takes place by the interaction of carbonmonoxide and hydrogen or by direct hydrogenation of carbon in thecarbonization zone. Under these conditions exothermic heat of reactionis released in the gasifier. Carbon which may be incidentally formed byreversal of the producer gas reaction or by the cracking of hydrocarbonsis carried by the carbonized solids to the gasification zone where it isregasified. Methane formation in the carbonization zone is influencedconsiderably by the composition of the carbonaceous feed material.Components of the ash, particularly iron, tend to catalyze themethanation reaction while sulfur compounds in the gas stream tend todeactivate the catalysts. The type of char made in the carbonizer alsoinfluences methane formation, lignite char being particularly active inthis respect and the cokes of coking coals being relatively inactive.

It will be evident from a consideration of the foregoing that thepresent invention provides utmost flexibility of operating conditions.The temperatures of operation of the gasiflcation and carbonizationzones are almost completely independent of one another. Furthermore, nocomplex arrangement of vessels and solid transfer equipment is requiredto obtain this important advantage. By reason of this flexibility anydesired type of gas: city gas, synthesis gas or pipe line gas may beproduced with high efiiciency.

The present process provides for passing any required quantity of theproduct gas from the gasifier to the carbonizer, forpassing any desiredquantity of carbonaceousmaterial from the gasifier to the carbonizer,and for removal of excess heat, if necessary, from the carbonizer.

Thus, a variety of feed materials may be handled.

For those feed materials which tend to catalyzethe disproportionation ofcarbon monoxide and formationofmethan'e, aminimum amount of heat may besupplied the carbonizer by gases, or solids, or both, from the gasifierand the temperature controlled by the heat exchanger. For those feedmaterials which have large heat requirements to'effect carbonization,such as those having high moisture contents or large percentages ofvolatile constituents or those which exhibit little or no tendency tocatalyze exothermic reactions like the methanation reaction, heatrequirements maybe readily satisfied by passing the required quantity ofhot solids, as well as gases, from the gasifier to the carbonizer. thetemperature of eachzone may be controlled independently of the other.

Gasification with oxygen and steam in the gasification zone preferablyis carried out. at a temperature within the range of about 1600 to 2000F. and at a pressure within the range of from about atmospheric to. 600pounds per square inch gauge, or even higher. Generally a pressurewithin the range of from about 200 to. about 500 pounds per square inchis preferred; The carbonization may be carried. out at temperatureswithin the range of from. about 900 F. to about 1300 F. and. atpressures comparable to those of the gasificatiorhzona; Pressures: andtemperature's may vary somewhat from these ranges and are not limitedthereto.

The following are examples of the application of the process of myinvention to the gasification of coal.

Example I A coal, crushed to a particle size such that 85 per centpasses a 100 mesh screen, is maintained in a feed hopper under apressure of 350 pounds per square inch gauge and fed at the rate of 10.5tons per hour into gasification equipment similar to that illustrated inFig. 1. Char from the carbonization zone at 1250 F. is recycled at arate of 52.5 tons per hour to a mixing zone where it is admixed with hotgases at 2000 F. from the gasification zone; the resulting mixture isadmixed with the incoming coal and passed to the carbonization zone. Thegasification zone is operated at a pressure of 350 pounds per squareinch gauge and the carbonization zone at a pressure of about 345 poundsper square inch gauge.

Char from the carbonization zone at a rate of 7.3 tons per hour is fedto the gasification zone in admixture with 1315 pounds of steam per hourat 375 pounds per square inch gauge and 1000 F. In addition, 4460 poundsof steam per hour in admixture with 225,000 standard cubic feet ofoxygen per hour at 300 F. is fed into the gasification zone. Thegasification zone is operated with a superficial gas velocity of about0.6 foot per second and a bed density of about 14 pounds per cubic foot.The velocity in the mixing zone is feet per second. The carbonizationzone is operated with a superficial gas velocity of 0.6 foot per secondand a. bed density of about 14 pounds per cubic foot.

A per cent carbon char is taken from the gasification zone at the rateof 2.67 tons per hour,

and utilized as fuel for production of steam requirements for the plant.885,000 standard cubic feet per hour of product gas is produced. Theproduct gas may be converted to synthesis feed gas by suitabletreatment, for example, removal or tar and oil, conversion ofhydrocarbon gases to carbon monoxide and hydrogen, conversion of carbonmonoxide and steam to hydrogen and carbon dioxide, and separation ofcarbon dioxide and sulfur.

Example II Gasification of coal at 1650 F. and 300 pounds per squareinch gauge is carried out in gasification equipment similar to thatillustrated in Fig. 2.

Coking coal of high volatile content which yields a relatively inactivechar is charged to the gasifier at the rate of 10 tons per hour bysuspension in a stream of recycle gas preheated to 900 F. The recyclegas stream is essentially a mixture of carbon monoxide, hydrogen, andlight hydrocarbons obtained as a residual gas after separation of tar,oil, water, and carbon dioxide from the product gases. Only sufficientrecycle gas is used as is required to transport the feed and recycledchar into the carbonizer.

The carbonizer is operated at 1250 F. and 280 pounds per square inchgauge. Product gases and hot char are passed from the gasifier to thecarbonizer. All of the product gas passes through the carbonizer. Justsuflicient carbonaceous material (or char) is passed from the gasifierto the carbonizer to satisfy the heat requirements in the carbonizer.Both the gasifier and carbonizer are operated under fluidized conditionsand fluid full. The carry over from the gasifier to the carbonizer andfrom the carbonizer to the separator is thus dependent upon the rate offeed to these zones.

About tons per hour of char is supplied to the carbonizer for admixturewith the fresh feed. Of this amount about 58 tons is recycled to thecarbonizer from the separator while about 42 tons is passed from thegasifier to the carbonizer.

About 108 tons per hour of carbonized material passes overhead from thecarbonizer to the separator. From the separator, the carbonaceousmaterial is returned to the gasification apparatus. One stream ofcarbonaceous material is sent to the carbonizer as the recycle char foradmixture with fresh feed and a second is sent to the gasifier.

About 1,100 pounds per hour is passed to an auxiliary generator operatedat 2300 F. for carbon cleanup and ash disposal. The carbon content ofthe carbonized material from the separator is about 50 per cent byweight.

The product gas is processed for the removal of water vapors,condensible oils and tar, and carbon dioxide. The resulting gas has atotal heating value of about 410 B. t. u. per cubic foot and thefollowing approximate analysis:

Volume per cent Hydrogen 35.2 Carbon monoxide 52.7 Methane 11.0 Nitrogen0.4 Illuminants 0.6

Gas is produced at the rate of about 570,000 standard cubic feet perhour. About 48,000 pounds per day of light oil and tar are separatedfrom the product gas stream. Steam at 900 F. is supplied to thegasification steps of the process at the rate of about 250,000 standardcubic feet per hour. Oxygen at 600 F. is supplied at the rate of about134,000 standard cubic feet per hour.

Obviously many modifications and variations of the invention ashereinabove set forth may be made without departin from the spirit andscop thereof and therefore only such limitations should be imposed asare indicated in the appended claims.

I claim:

1. A process for the carbonization and gasification of solidcarbonaceous material containing volatilizable constituents whichcomprises maintaining a dense phase fluidized bed of particles of solidcarbonaceous material in a carbonization zone wherein volatilizableconstituents are distilled from said particles producing carbonizedmaterial, passing carbonized material from said carbonization zone to aseparate gasification zone, subjecting said carbonized material toreaction with oxygen and steam in said gasiflcation zone to produce aprimary gas consisting essentially of carbon monoxide and hydrogen,passing a stream of said primary gas through an intermediate zone ofrestricted cross-sectional area directly into the lower portion of saidcarbonization zone thereby effecting fiuidization of the carbonaceousmaterial therein and distillation of said volatilizable constituents,introducing particles of fresh carbonaceous material containingvolatilizable constituents into said stream of primary gas in saidintermediate zone, introducing particles of carbonized materialsubstantially free from volatilizable constituents from saidcarbonization zone directly into said stream of primary gas in saidintermediate zone upstream from the point of introduction of said freshcarbonaceous material and in controlled amounts whereby at least 3 partsby weight of carbonized material is added per part of said freshcarbonaceous material, maintaining the velocity of said stream ofprimary ga through said intermediate zone at a velocity suiiicient toentrain said particles of said fresh and carbonized material therein,and discharging from said carbonization zone the resulting gascontaining volatilized constituents and products of reaction.

2. A process as defined in claim 1 wherein said dense phase fluidizedbed of solid particles maintained in said carbonization zonesubstantially completely fills said carbonization zone whereby 15particles of carbonized material are entrained in gases discharged fromsaid carbonization zone, carbonized material separated from gasesdischarged from said carbonization zone, a portion of the separatedcarbonized material passed directly to said intermediate zone, and afurther 10 portion of the separated carbonized material passed to saidgasiflcation zone.

JOHN C. KALBACH.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,094,946 Hubmann Oct. 5, 1937 2,111,579 Winkler Mar. 22, 19382,534,728 Nelson et a1 Dec. 19, 1950 2,582,711 Nelson Jan. 15, 1952FOREIGN PATENTS Number Country Date 286,404 Great Britain Mar. 8, 1928578,711 Great Britain July 9, 1946 582,055 Great Britain Nov. 4, 1946OTHER REFERENCES Kalbach, Chemical Engineering, vol. 54, pages 105-408,January, 1947.

1. A PROCESS FOR THE CARBONIZATION AND GASIFICATION OF SOLIDCARBONACEOUS MATERIAL CONTAINING VOLATILIZABLE CONSTITUENTS WHICHCOMPRISES MAINTAINING A DENSE PHASE FLUIDIZED BED OF PARTICLES OF SOLIDCARBONACEOUS MATERIAL IN A CARBONIZATION ZONE WHEREIN VOLATILIZABLECONSTITUENTS ARE DISTILLED FROM SAID PARTICLES PRODUCING CARBONIZEDMATERIAL, PASSING CARBONIZED MATERIAL FROM SAID CARBONZATION ZONE TO ASEPARATE GASIFICATION ZONE, SUBJECTING SAID CARBONIZED MATERIAL TOREACTION WITH OXYGEN AND STREAM IN SAID GASIFICATION ZONE TO PRODUCE APRIMARY GAS CONSISTING ESSENTIALLY OF CARBON MONOXIDE AND HYDROGEN,PASSING A STREAM OF SAID PRIMARY GAS THROUGH AN INTERMEDIATE ZONE OFRESTRICTED CROSS-SECTIONAL AREA DIRECTLY INTO THE LOWER PORTION OF SAIDCARBONIZATION ZONE THEREBY EFFECTING FLUIDIZATION OF THE CARBONACEOUSMATERIAL THEREIN AND DISTILLATION OF SAID VOLATILIZABLE CONSTITUENTS,INTRODUCING PARTICLES OF FRESH CARBONACEOUS MATERIAL CONTAININGVOLATILIZABLE CONSTITUENTS INTO SAID STREAM OF PRIMARY GAS IN SAIDINTERMEDIATE ZONE, INTRODUCING PARTICLES OF CARBONIZED MATERIALSUBSTANTIALLY